Deep Back Muscles – Back Muscles

00:00 The deep back muscles, which are known as intrinsic or true back muscles, these muscles are going to originate and attach on back related structures meaning that they are not going to have an attachment outside of the axial skeleton as did the other muscles that we discussed.

00:23 In addition your deep or intrinsic or true back muscles are going to be innervated by posterior rami of spinal nerves. These muscles are going to be arranged into three layers - superficial, these superficial muscles can also be termed as spinotransversales muscles, we have an intermediate group of deep back muscles, these constitute the erector spinae and we also have several muscles that are characterized as being deeply layered within the deep back musculature.

01:05 Here we are looking at the muscles that constitute the superficial layer of the deep back musculature, these are also members of that spinotransversales group and if we think a moment about the name what this informs us is, these are points of attachment. They are going to attach generally from the spines of your vertebrae to the transverse processes of the vertebrae. The two muscles that fall within this category or this layer are your splenius capitis and your splenius cervices.

01:49 Here is your splenius capitis and through here and your cervices is running as a narrow band of musculature out here more laterally. When we take a look at the splenia and we kind of look at these collectively, we will want to understand their attachments, their innervation and their action.

02:18 For attachments, the splenius capitis is going to attach more inferiorly along the lower portion of your ligamentum nuchae, it is also going to attach to the spinous processes of C7, usually down to the level of T4. The insertion of your capitis, as the name implies, is going to be to the skull or to the head that will be to the mastoid process of the skull as well as to an area just below the superior nuchal line.

02:56 The innervation will be posterior rami, nothing more specific than that and the action of your splenius capitis, if both are acting, so bilateral contraction. It will pull your head posteriorly because of its attachments to the skull. If it’s acting unilaterally which is, say the right one is contracting, it will tilt the head and flex the neck to that same side.

03:26 The splenius cervices, again, is going to be along here, more of a narrow band. It’s hard to really discern it as a separate muscle mass, but it too will originate from the spinous processes and it generally will originate from T3 down to T6. The insertion of your cervices will be to the cervical vertebrae specifically the transverse processes of C1, C2 and C3.

03:59 Innervation again will be the same - posterior rami in this particular region, the action will be very, very similar to that of the capitis. Bilateral will extend the neck and where the neck goes, the skull tends to follow. If it’s unilateral contraction, it’s just that the right splenius cervices contracting, it will laterally flex the neck to the same side and it can also help to rotate the neck and the head to the same side.

04:32 Now, we are transitioning to the intermediate layer of the deep back musculature and the intermediate muscles that we have here collectively form the erector spinae group. The erector spinae muscles are arranged into three columns and we can appreciate all three columns in this particular illustration.

05:02 The most lateral column which we see here and being reflected here on the left side of the image, this column is your iliocostalis muscle column. The one here in the middle, that’s better exposed and the one over here is the longissimus muscle column. And the most medial shown here and a little more clearly here on the opposite side is the spinalis.

05:36 Each one of these columns is described as being subdivided - the iliocostalis can be divided into a lumbar component, a thoracic component and the more superior division of your iliocostalis will be the cervical division. The longissimus is also divided into three divisions - there is a thoracic area or region of it, more superiorly there is a cervical component and it also will then have a capitis component because the more superior muscle components of this column attach to the skull. The spinalis column, the best division of it is in the thoracic area, but textbooks will describe it as also having a cervical component and a more superior component that attaches to the skull, hence a capitis subdivision.

06:45 Now, we will take a look at each one of these columns of the erector spinae muscle group.

06:59 I will start with the most lateral column that being the iliocostalis. There is a lot of detail that involves attachments. So, we will try to kind of simplify this to some degree, but let’s think a moment about the name and what the name implies, iliocostalis, the ilium informs us or the ilial tells us something about the ilium and inferior points of attachment, the suffix costalis informs us that there are attachments to the ribs.

07:34 So, the more inferior attachments of your iliocostalis muscle column will be down at the level of ilium as well as the sacrum and then there will be some attachments to the ribs more inferiorly and then some of the other subdivisions of this column as we move upwards along the back. What will happen is the more inferior subdivisions of this column will originate from the lower ribs with more superior attachments to the upper ribs.

08:11 In the cervical area, these upper fibers will originate from the upper ribs and then subsequently attach to the transverse processes of some of the cervical vertebrae. Innervation is simply posterior rami. Again, these are true back muscles, so we won’t make it anymore difficult than that.

08:36 The action of the iliocostalis is shared with the other columns of the erector spinae when working bilaterally. These are strong extenders of the vertebral column, if it’s working unilaterally, so you have the right iliocostalis or any other member of the right sided erector spinae group contracting with the exception of the spinalis, you can also get some lateral banding or flexion to the trunk of the body.

09:15 The longissimus muscle column and, again, are much more detailed than you really need to know regarding the attachments of this muscle group, you can think of this muscle column running from transverse process to more superior transverse processes. Certainly, as you get up with the capitis division, that most superior division of your longissimus, there you are looking at the division that attaches to the skull going to the mastoid process.

09:51 So, think of this as jumping from transverse process to transverse process in contrast to the iliocostalis that’s jumping from rib to more superior ribs, generally speaking.

10:05 Innervation, again, is going to be the posterior rami. Action is going to be shared with the iliocostalis group - bilateral, you are going to extend; unilateral, you are flexed to the same side.

10:25 Here we are looking at the medial most column of the erector spinae group, the spinalis.

10:34 This one take-home message for attachments would be it's jumping from spinous process to more superior spinous processes. Hence the name spinalis. Innervation is going to, again, be posterior rami. Action, these aren’t nearly as well developed as the other two columns, but certainly working bilaterally, the spinalis columns can help with erecting or extending the vertebral column; unilateral action because of their spinous process to spinous process attachment is minimal to non-existent.

11:19 This side depicts the muscles that belong to the deep layer, the deep back musculature.

11:28 It’s quite an extensive list of what we see here are three different types of semi spinalis muscles, a capitis, a cervices and a thoracis. We also have the multifidus, we have long and short rotators known as the rotatores longus and the rotatores brevis.

11:52 And then we have the interspinalis muscles, the intertransversarii muscles and then lastly, in this group, we have the levatores costarum muscles.

12:05 If we take a look at the rotatores and everything above that, all of these muscles that we see here are members of a muscle group called the transversospinalis muscle group and that name implies they are points of attachment. These muscles generally are going to attach to the more lateral transverse processes of vertebrae and then they will run superiorly and medially to attach to spinous processes. So, that is the kind of a take-home message there if we want to kind of boil it down to the basics.

12:51 The interspinalis, the intertransversarii, the levatores these muscles are known as segmental muscles. We are not going to talk about all these muscles in any great detail with the exception of the first two, the semispinalis capitis and the semispinalis cervices.

13:16 So, here we see an illustration that is demonstrating the semispinalis capitis and the semispinalis cervices. The capitis is this muscular band that we see in through here, for example and then on the opposite side of the illustration, it has been cut and reflected and it is an appreciably thick muscle mass, much more than we really think when we are actually doing a dissection of the cervical area. But, if we reflect the semispinalis capitis, we can see the muscle fibers of the semispinalis cervices and the most superior point of attachment of the semispinalis cervices is going to be on the spinous process of C2.

14:18 Now, let’s take a look at the attachments, innervation and action of the semispinalis capitis muscle, the attachments of this muscle and we see, again, the muscle right in through here are going to be from the transverse processes of T1 and T6. So, we will be down here in the more inferior region of the illustration, it’s also going to have points of origin from the articular processes of C4, 5 and 6 Insertion, we see that insertion occurring to the base of the skull.

15:00 This is going to be located between the superior and inferior nuchal lines of the occipital bone. Innervation is going to be by posterior rami and then the action of this muscle will be, if it’s acting bilaterally, it will help to extend the head, pull it backwards, it will pull the cervical vertebrae with it and help to extend the neck. If it’s acting unilaterally and it’s the left one, let’s say, it will help rotate it to the same side.

15:42 The semispinalis cervices is lying deep to the capitis and so, we see several of the muscle fibers of this muscle within this particular region, the semispinalis cervices is going to originate from the transverse processes of the upper 5 or 6 thoracic vertebrae and then it will insert onto the spinous processes of C2 and some of these cervical vertebrae below.

16:20 Innervation of the semispinalis cervices will be posterior rami. The action of this muscle, if it’s acting bilaterally, will be to help extend the neck and if this muscle is contracting unilaterally, let’s say, it’s the right one, as it would be in this illustration right in through here, it will rotate the head and neck to the opposite side.

16:55 As mentioned before, there are other members of the deep group of deep back muscles, multifidus, the rotatores, interspinalis, intertransversarii, levatores costarum, they are depicted here and I will just point them out to you quickly. If you wish to learn more about these on your own, you are certainly encouraged to do so, but your multifidus muscle mass is best developed down in through here in the lower lumbar and sacral region does extend superiorly along the vertebral column.

17:34 The rotators are seen in through here, here is the long one and then the short one is running just medial to it. Your interspinalis muscles are best seen here in the more superior view and they run from spinous process to spinous process and they are bilateral, see you see one and one on the other side as well. Intertransversarii, we see some examples of them in this area, very delicate slender muscles running from transverse process to transverse process. We also see our levatores costarum and you can see, as the name would imply, they have to have attachment to the ribs because of the costarum portion of their name and you see those costal or rib attachments along and through here.

18:32 Now, we will shift our attention to a region of the posterior cervical area between the